1. Field of the Invention
The present invention relates to an improved apparatus for controlling an auxiliary steering mechanism of an automotive vehicle. More specifically, the present invention relates to an auxiliary steering control arrangement wherein deviations which are produced by erroneous sensing of the rotation of a steering wheel with respect to its neutral or home position, are corrected at a controlled rate so as to avoid sudden changes in the steering angle of the auxiliary steering mechanism.
2. Description of the Prior Art
In the art of vehicular steering mechanisms, auxiliary steering mechanisms have been proposed for the purpose of improving both high speed cornering and low speed maneuverability of a vehicle. In these systems the auxiliary steering mechanisms are provided in connection with at least two of the vehicle's wheels, such as the rear wheels. An example of such a system is given in JP-A-61-41676.
The steering angle of the auxiliary steering mechanism is controlled on the basis of a detected steering wheel angle and according to the speed of the vehicle.
Generally, in such systems, a pulse counting means, which includes a light source/shutter type arrangement or the like, is operatively connected with the steering wheel or steering shaft. The pulses are counted by the pulse counting means as the steering wheel is rotated from its neutral position, in order to determine the amount of rotation of the wheel and the angle to which it is desired to turn the steering wheels of the vehicle. This pulse counting means is designed to provide a signal which is indicative of the angular disposition of the steering wheel and which forms a basis for the control of the auxiliary steering mechanism.
In such a system it is conceivable to perform all subsequent steering angle determinations by continuously updating the detected steering wheel angle, on the basis of the number of pulses which are counted up or down from the last detected angular position of the steering wheel.
However, in such pulse count type steering wheel angle detection arrangements it sometimes happens that when the steering wheel is very rapidly rotated, the pulses are erroneously counted. This results in the steering wheel being indicated as being in a position other than the one it is actually in. Thus, if the steering angle detected by the pulse counting means, is simply updated perpetually on the basis of the number of pulses counted, there is a tendency for any error generated during a sensing operation to carry over into all subsequent steering angle sensing operations.
In order to avoid the latter problem, the sensing means is arranged such that a signal is generated each time the steering wheel is returned to its home or neutral position. Upon receipt of this signal the auxiliary steering mechanism is induced to produce a zero steering condition.
While this arrangement eliminates the possibility of cumulative errors being generated and sustained in the steering wheel angle sensing mechanism, it induces the problem that, regardless of the magnitude of error in the sensed position of the steering wheel, when the steering wheel returns to or passes through the neutral position the auxiliary steering mechanism is induced to return immediately to its neutral steering state.
Accordingly, when the steering wheel is returned to its the neutral position, there is the possibility that an error may be cancelled and a sudden change be produced in the steering angle of the auxiliary steering. This tends to expose the vehicle occupants to the dangers accompanying unpredictable steering response, as well as giving the driver an alarming sense incongruity in the vehicular handling characteristics. This danger is particularly pronounced at high vehicular speeds, whereat even slight changes in the steering angle, can have a pronounced effect.